Accidental aquatic biology in an aquarium

In the biology lab we have had an aquarium for keeping aquatic plants for probably about six years.  All was going well until about two years ago when we purchased some aquatic plants from a new vendor.  These new plants were unfortunately inhabited by a few hidden snails.  Resulting in a snail population explosion in our tank.  The snail population probably peaked somewhere around several hundred snails in our ten gallon tank.  Large bunches of the aquatic plant elodea could be eaten in a matter of days by these snails.  We fought this snail population for about two years by trying to starve them to death, but ultimately it was unsuccessful. 

Snail on the side of our fish tank.

Snail eggs on the side of our fish tank.

 Thinking that maybe snails were coming in on each of our shipments of aquatic plants we tried a new vendor.  Well this third vendor was worse than the previous one.  Snails still proliferated in the tank but apparently mosquito eggs or larva, and some sort of daphnia zooplankton came in with our latest shipment of plants.  This resulted in a rather large swarm of mosquitoes in our tank and huge numbers of daphnia swimming around in the water.  Fortunately, we had a good lid on the tank so the mosquitoes did not escape.

Mosquito larva in our tank.  The tiny dots are either sediment or tiny daphnia swimming around.

As a result of all this we finally had to dump the tank out and start over.  But in the process we got to observe some pretty interesting things: snail and mosquito life cycles, exponential population growth and subsequent crash, control of food on the snail population, and even some microbiology.  A pretty cool accidental aquatic biology experiment if I don't say so myself.  Next time we are going to stick with our first vendor, and if we have the same problem I think we'll introduce a small fish into the tank to see what happens.